全文获取类型
收费全文 | 156篇 |
免费 | 2篇 |
国内免费 | 2篇 |
学科分类
数理化 | 160篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 2篇 |
2019年 | 5篇 |
2018年 | 2篇 |
2017年 | 5篇 |
2016年 | 9篇 |
2015年 | 5篇 |
2014年 | 2篇 |
2013年 | 7篇 |
2012年 | 10篇 |
2011年 | 13篇 |
2010年 | 9篇 |
2009年 | 5篇 |
2008年 | 9篇 |
2007年 | 8篇 |
2006年 | 10篇 |
2005年 | 10篇 |
2004年 | 9篇 |
2003年 | 3篇 |
2002年 | 7篇 |
2001年 | 11篇 |
2000年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有160条查询结果,搜索用时 156 毫秒
51.
Offline and online fatigue crack growth prediction of Aluminum 2024 compact-tension (CT) specimens under variable loading has been modeled, using multivariate Gaussian Process (GP) technique. The GP model is a Bayesian statistic stochastic model that projects the input space to an output space by probabilistically inferring the underlying nonlinear function. For the offline prediction, the input space of the model is trained with parameters that affect fatigue crack growth, such as the number of fatigue cycles, minimum load, maximum load, and load ratio. For the online prediction, the model input space is trained using piezoelectric sensor signal features rather than training the input space with loading parameters, which are difficult to measure in a real time scenario. Principal Component Analysis (PCA) is used to extract the principal features from sensor signals. In both the offline and online case, the output space is trained with known associated crack lengths or crack growth rates. Once the GP model is trained, a new output space for which the corresponding crack length or crack growth rate is not known, is predicted using the trained GP model. The models are validated through several numerical examples. 相似文献
52.
A diuretic is a substance widely prohibited in competition sports, by the World Anti-Doping Agency (WADA). In this paper, a sensitive, rapid and convenient analytical solid phase extraction-fluorimetric method for the determination of furosemide (FUR) and amiloride hydrochloride (AMI) diuretics in human urine was developed. FUR and AMI exhibit overlapped fluorescent spectra and urine produces background fluorescence that precludes the direct determination of these diuretics by conventional fluorimetry. AMI was adsorbed using nylon membranes whereas; FUR was detected in aqueous solutions. The optimum analytical conditions for AMI and FUR assay were established. Excitation wavelengths of 365 nm and 237 nm and emission wavelengths of 406 and 415 nm were used for AMI and FUR, respectively. The calibration graphs are linear in the range of 3.7 × 10−4 to 0.8 μg mL− 1 and 1.2 × 10− 3 to 4.0 μg mL− 1, for AMI and FUR, respectively, with a detection limit of 1.1 × 10− 4 and 3.5 × 10− 4 μg mL− 1 (S/N = 3). These concentrations correspond well with the range of the drugs in urine. AMI and FUR were accurately quantified in doped urine samples and urine of subjects under medical treatment with diuretic. The results were validated by recovery test, being highly satisfactory. 相似文献
53.
We demonstrate that the polarization states of guided wave surface plasmon polariton (SPP) modes can be unambiguously identified by introducing a linear polarizer in the optical path of the light within a leakage-based microscope. We show the use of Fourier-plane leakage-based microscopy as a polarization characterization method to study the polarization states of SPP modes excited in plasmonic waveguides. Our results indicate that the inclusion of a linear polarizer provides additional image processing capabilities to leakage-based microscopes. 相似文献
54.
55.
We have implemented a Gaussian basis-set two-component self-consistent field method based on the fourth-order nuclear-only Douglas-Kroll-Hess approximation. Two-electron spin-orbit effects are included using Boettger's screened-nuclear spin-orbit approximation. In our two-component approach, the spin-orbit interaction is taken into account in a variational fashion employing a generalized Kohm-Sham scheme which allows one to work with hybrid density functionals. For open-shell systems we adopt the noncollinear spin-density approximation. Results are presented for equilibrium bond lengths, harmonic vibrational frequencies, and bond dissociation energies with local spin-density, generalized gradient approximation, and hybrid functionals in a set of benchmark molecules. 相似文献
56.
We have employed the Douglas-Kroll-Hess approximation to derive the perturbative Hamiltonians involved in the calculation of NMR spin-spin couplings in molecules containing heavy elements. We have applied this two-component quasirelativistic approach using finite perturbation theory in combination with a generalized Kohn-Sham code that includes the spin-orbit interaction self-consistently and works with Hartree-Fock and both pure and hybrid density functionals. We present numerical results for one-bond spin-spin couplings in the series of tetrahydrides CH(4), SiH(4), GeH(4), and SnH(4). Our two-component Hartree-Fock results are in good agreement with four-component Dirac-Hartree-Fock calculations, although a density-functional treatment better reproduces the available experimental data. 相似文献
57.
Jaime Wisniak Gladis Cortez René D. Peralta Ramiro Infante Luis E. Elizalde 《Journal of solution chemistry》2007,36(8):997-1022
Densities of the binary systems of toluene with butyl methacrylate, allyl methacrylate, methacrylic acid, and vinyl acetate
have been measured as a function of composition at 20, 30 and 40 °C at atmospheric pressure, using an Anton Paar DMA 5000
oscillating U-tube densimeter. The excess molar volumes are negative for the system toluene + butyl methacrylate and positive
for the three other binaries, and become more so as the temperature increases from 20 to 40 °C. The system toluene + allyl
methacrylate presents near ideal behavior. The apparent volumes were used to calculate values of the partial excess molar
volumes at infinite dilution. The excess coefficient of thermal expansion is positive for the four binary systems. The calculated
excess molar volumes were correlated with the Redlich–Kister equation and with a series of Legendre polynomials. An explanation
of the results is given based by the FT-IR (ATR) and 13C NMR spectra of equimolar mixtures of the different systems. 相似文献
58.
Batista ER Martin RL Hay PJ Peralta JE Scuseria GE 《The Journal of chemical physics》2004,121(5):2144-2150
The structural properties and thermochemistry of UF6 and UF5 have been investigated using both Hartree-Fock and density functional theory (DFT) approximations. Within the latter approach, the local spin-density approximation, the generalized gradient approximation, and hybrid density functionals were considered. To describe the uranium atom we employed small-core (60 electrons) and large-core (78 electrons) relativistic effective core potentials (RECPs), as well as the all-electron approximation based on the two-component third-order Douglas-Kroll-Hess Hamiltonian. For structural properties, we obtained very good agreement with experiment with DFT and both large and small-core RECPs. The best match with experiment is given by the hybrid functionals with the small-core RECP. The bond dissociation energy (BDE) was obtained from the relative energies of the fragments [UF6 --> UF5 + F], corrected for zero-point energy and spin-orbit interaction. Very good agreement was found between the BDE obtained from all-electron calculations and those calculated with the small-core RECP, while those from the large-core RECP are off by more than 50%. In order to obtain good agreement with experiment in the BDE it is imperative to work with hybrid density functionals and a small-core RECP. 相似文献
59.
de Kowalewski DG Díez E Esteban AL Barone V Peralta JE Contreras RH 《Magnetic resonance in chemistry : MRC》2004,42(11):938-943
One- two- and three 13C, 13C (n = 1, 2, 3) scalar couplings, (n)J(C,C) in a set of pyrimidine derivatives were studied both experimentally at natural abundance and theoretically by their DFT calculation of all four contributions. Trends of non-contact terms are discussed and substituent effects are rationalized, comparing some of them with the corresponding values in benzene and pyridine. Although substituent effects on non-contact terms are relatively important, the whole trend is dominated by the Fermi contact term. According to the current literature, substituent effects on 1J(C,C) couplings in benzene derivatives are dominated by the inductive effect, which, apparently, is also the case in nitrogen heteroaromatic compounds. However, some differences observed in this work for substituent effects on 1J(C,C) couplings in pyrimidine derivatives suggest that in the latter type of compounds substituent effects can be affected by the orientation of the ring nitrogen lone pairs. 相似文献
60.
Jaime Wisniak Lidia E. Sandoval René D. Peralta Ramiro Infante Gladis Cortez Luis E. Elizalde Homero Soto 《Journal of solution chemistry》2007,36(1):135-152
Densities of the ternary system, ethylbenzene + styrene + ethyl acrylate, and its three binaries have been measured in the
whole composition range at 298.15 K and atmospheric pressure using an Anton Paar DMA 5000 oscillating U-tube densimeter. The
calculated excess molar volumes are positive for the binary system, ethylbenzene + ethyl acrylate, and negative for the systems
ethylbenzene + styrene and styrene + ethyl acrylate. The corresponding data were correlated with the Redlich-Kister equation
and with a series of Legendre polynomials. Several models were used to correlate the ternary behavior from the excess molar
volume data of their constituent binaries and were found to fit the data equally well. The best fit was based on a direct
approach, without information on the component binary systems. 相似文献